This invention pertains generally to the field of assays for biological and chemical substances and more specifically to blocking layers for use in liquid crystal assays.
Methods for detecting the presence of biological substances and chemical compounds in samples has been an area of continuous development in the field of analytical chemistry and biochemistry. Various methods have been developed that allow for the detection of various target species in samples taken from sources such as the environment or a living organism. Detection of a target species is often necessary in clinical situations before a prescribed method of treatment may be undertaken and an illness diagnosed.
Several types of assay currently exist for detecting the presence of target species in samples. One conventional type of assay is the radioimmunoassay (RIA). RIA is a highly sensitive technique that can detect very low concentrations of antigen or antibody in a sample. RIA involves the competitive binding of radiolabeled antigen and unlabeled antigen to a high-affinity antibody. Typically, the labeled antigen is mixed with the antibody at a concentration that just saturates the antigen-binding sites of the antibody molecule. Then, increasing amounts of unlabeled antigen of unknown concentration are added. Because the antibody does not distinguish between labeled and unlabeled antigen, the two types of antigen compete for the available binding sites on the antibody. By measuring the amount of labeled antigen free in solutions, it is possible to determine the concentration of unlabeled antigen. Kuby, J., Immunology, W. H. Freeman and Company, New York, N.Y. (1991), pp. 147-150.
Another type of assay which has become increasingly popular for detecting the presence of pathogenic organisms is the enzyme-linked immunosorbent assay or ELISA. This type of assay allows pathogenic organisms to be detected using biological species capable of recognizing epitopes associated with proteins, viruses and bacteria. Generally, in an ELISA assay, an enzyme conjugated to an antibody will react with a colorless substrate to generate a colored reaction product if a target species is present in the sample. Kuby, J., Immunology, W. H. Freeman and Company, New York, N.Y. (1991), pp. 147-150. Physically adsorbed bovine serum albumin has been used in various such assays as a blocking layer because it has been found to prevent the non-specific adsorption of biological species that might interfere with or result in erroneous assay results.
Although ELISA and other immunosorbent assays are simple and widely used methods, they have several disadvantages. Tizard, I. R. Veterinary Immunology: An Introduction, W. B. Saunders Company, Philadelphia, Pa. (1996); Harlow, Ed.; Lane, D. Antibodies: A Laboratory Manual, Cold Springs Harbor Laboratory, Cold Springs Harbor, N.Y. (1988); Van Oss, C. J.; van Regenmortel, M. H. V. Immunochemistry, Dekker, New York, N.Y. (1994). Labeled antibodies can be expensive, especially for assays requiring radioactive labels. Additionally, radioactive labels require special handling as radioactive materials are also hazardous. The labeling of a compound, which is the main drawback of these methods, may alter the binding affinity of antibody to analyte. Enzymes are large molecules that may sterically inhibit antibody activity or it may lose enzymatic activity after conjugation to antibodies. Another concern with immunosorbent assays is non-specific binding of proteins to the solid support, antigen, and antibody complexes. This can lead to an increase in background noise, loss of sensitivity, and potentially a false positive test result. Additionally, the immobilization of proteins on the solid support can affect the conformation of the binding sites, leading to a decrease in sensitivity, and possible increase in non-specific binding. For example, physical adsorption of proteins to polystyrene wells occurs due to hydrophobic interactions between the protein and solid support. These interactions can also promote unfolding of the amino acid chains in order to cover the polystyrene surface. This can lead to possible inactivation of the binding sites.
Qualitative diagnostic assays based on aggregation of protein coated beads can also be used for the detection of proteins and viruses. Tizard, I. R. Veterinary Immunology: An Introduction, W. B. Saunders Company, Philadelphia, Pa. (1996): Cocchi, J. M.; Trabaud, M. A.; Grange, J.; Serres, P. F.; Desgranges, C. J. Immunological Meth., 160, (1993), pp. 1; Starkey, C. A.; Yen-Lieberman, B.; Proffitt, M. R. J. Clin. Microbiol., 28, (1990), pp. 819; Van Oss, C. J.; van Regenmortel, M. H. V. Immunochemistry, Dekker, New York, N.Y. (1994). For direct detection of antibodies, antigen is non-specifically adsorbed to the surface of latex beads which are several microns in diameter. The protein-coated beads possess a slight charge which prevents aggregation. Introduction of an antibody specific to the adsorbed protein can link the beads, leading to agglutination. The agglutination can be detected by eye or by other methods such as quasi-elastic light scattering. Visual agglutination assays, however, are not sensitive and measurement by quasi-elastic light scattering requires complex apparatus and is not suitable for use in locations remote from central labs. Furthermore, it is not possible to perform highly multiplexed agglutination assays using microarrays because of the bulk solution methodology of this type of assay.
To overcome the need for labeled proteins, principles based on direct detection of the binding of proteins and ligands have been investigated. Schmitt, F.-J.; Haussling, L.; Ringsdorf, H.; Knoll, W. Thin Solid Films, 210/211, (1992), pp. 815; Hauslling, L.; Ringsdorf, H. Langmuir, 7, (1991), pp. 1837. Surface plasmon reflectometry (SPR) is one such method. SPR is sensitive to changes in the index of refraction of a fluid near a thin metal surface that has been excited by evanescent electromagnetic waves. The binding of proteins to ligands can be detected by examining an increase in the resonance angle or intensity of signal. Typical angular resolution using this method is 0.005xc2x0 allowing detection of sub-angstrom changes in adsorbed film thickness with SPR. However, care must be taken to ensure that the change in resonance angle is due to binding and not just a change in the bulk solution index of refraction. A thermally stable environment is required due to the dependence of the resonance angle on the index of refraction of the fluid. An increase in temperature from 25xc2x0 C. to 26xc2x0 C. in water amounts to a change in the index of refraction by 0.0001. This increase would result in the change in resonance angle of approximately 0.015xc2x0 or roughly 0.2 nm in the observed height of a protein layer. This temperature stability requirement makes SPR unsuitable for most field applications. In addition, non-specific adsorption of molecules on to or near the sensor surface can lead to false changes in signal, requiring a surface which minimizes non-specific interactions. Therefore, surface plasmon reflectivity is more complex than ELISA, requires laboratory based equipment, and the preparation of a well defined surface.
The use of ion-channel switches for detecting biospecific interactions has been reported. Cornell, B. A.; Braach-Maksvytis, V. L. B.; King, L. G.; Osman, P. D. J.; Raguse, B.; Wieczorek, L.; Pace, R. J. Nature, 387, (1997), pp. 580. In a device using ion channel switches, a tethered lipid membrane incorporating mobile ion channels is separated from a gold electrode surface by an ion reservoir. The gold surface serves as an anchor for the membrane and acts as an electrode. Within the membrane are upper and lower ion channels. In order to become conductive, the outer and inner ion channels must align and form a dimer. Membrane spanning lipids, which help stabilize the lipid membrane, are attached at one end to the electrode surface and are terminated with ligands that extend away from the membrane. The ion channels of the outer layer possess ligands. Unbound, the outer ion channels move freely, occasionally forming dimers with the inner channels, allowing conduction. The binding of a bivalent molecule to both the ion channel and membrane spanning lipid restricts the mobility of the outer ion channel, leading to a measurable decrease in conductivity. However, if a large amount of protein adsorbs to the outer layer, the ion channel mobility presumably would be restricted and a false decrease in conductance could be observed due to non-specific interactions. Additionally, this method requires sensitive devices for detecting the change in conductance. The procedure for fabricating the membranes requires several hours and the membrane stability is limited (must be immersed in solution). More importantly, specific antibodies must be attached to the membrane/channels, requiring separate protein chemistry for each analyte to be detected.
A method based on a porous silicon support that permits optical detection of the binding of specific proteins to ligands has been reported. Lin, V.; Motesharei, K.; Dancil, K. S.; Sailor, M. J.; Ghadiri, M. R. Science, 278, (1997), pp. 840; Dancil, K. S.; Greiner, D. P.; Sailor M. J. J. Am. Chem. Soc., 121, (1999), pp. 7925. The porous areas are typically 1 to 5 xcexcm deep and a few square micrometers to millimeters in area. Typical binding times are on the order of 30 minutes followed by rinsing of the surface. Initial work in this area incorrectly reported the detection of extremely low concentrations of analyte. Binding of streptavidin to biotinylated surfaces was initially found to reduce the index of refraction of the porous support, however this was later correctly attributed to surface oxidation. In addition, a change in the effective optical thickness of the film was reportedly observed upon introduction of streptavidin, however, differentiation between specific interactions and non-specific adsorption could not be made. This method does not require labeled molecules, however, the porous silicon surface is susceptible to oxidation and non-specific adsorption.
The use of polymerized multilayer assemblies for the detection of receptor-ligand interactions has also been reported. Charych, D. H.; Nagy, J. O.; Spevak, W.; Bednarski, M. D. Science, 261, (1993), pp. 585; Pan, J. J.; Charych, D. Langmuir, 13, (1997), pp. 1365. Polydiacetylene multilayer films deposited by Langmuir-Blodgett technique change color from blue to red due to a conformational change in the polymer backbone. For example, changes in temperature or pH can cause a shift in color. The response can be controlled and used for protein detection by attaching ligands to the multilayer. Upon binding of a multivalent macromolecule to ligands, stress is introduced into the multilayer assembly. A change in color is seen in the system if sufficient protein is bound, with binding times typically on the order of 30 minutes. This system permits direct detection of receptor-ligand interactions and transduces the events into an optical signal that can be easily measured and quantified. The optical output can be interpreted by eye or analyzed with a spectrophotometer for quantitative conclusions. The use of polymerized multilayer assemblies for the detection of influenza virus has been demonstrated. A significant disadvantage of this method, however, is that it requires multi-valent analyte. Multiple ligands connected to the polymerized multilayer must attach to the same macromolecule. This prevents the use of this method for monovalent molecules (even bead based assays can be performed competitively, not requiring multivalent molecules). Binding of bivalent molecules such as IgG""s has not been demonstrated. Furthermore, Langmuir-Blodgett deposition is a process which is difficult to translate from laboratory to commercial scale. As an alternative method to Langmuir-Blodgett deposition, these principles has also been demonstrated using vesicles. However, research based on vesicles, reveals the usefulness of the system to be limited because it is insensitive to the analyte at concentrations below 0.1 mg/ml.
Although many of the conventional assay methods described above work very well to detect the presence of target species, many conventional assay methods are expensive and often require instrumentation and highly trained individuals, which makes them difficult to use routinely in the field. Thus, a need exists for assay devices and systems which are easier to use and which allow for evaluation of samples in remote locations.
Recently, assay devices that employ liquid crystals have been disclosed. For example, a liquid crystal assay device using mixed self-assembled monolayers (SAMs) containing octanethiol and biotin supported on an anisotropic gold film obliquely deposited on glass has recently been reported. Gupta, V. K.; Skaife, J. J.; Dubrovsky, T. B., Abbott N. L. Science, 279, (1998), pp. 2077-2079. In addition, PCT publication WO 99/63329 published on Dec. 9, 1999, discloses assay devices using SAMs attached to a substrate and liquid crystal layer that is anchored by the SAM.
Although the disclosed liquid crystal-based assay devices which use anisotropic gold films are suitable for use in determining whether a target species is present in a sample, the preparation of the anisotropic gold film by oblique deposition is difficult. For example, the preparation of obliquely deposited gold films requires complicated cleaning steps and high vacuum deposition. Therefore, a need exits for a substrate structure which is easy to prepare and which resists non-specific adsorption by proteins which could result in false positive test results.
The present invention provides rubbed substrate structures for use in a liquid assay device, optical cells prepared using the rubbed substrate structures, methods for preparing the rubbed substrate structures, kits for use in a liquid crystal assay, and methods for detecting a target species using a liquid crystal assay device.
A rubbed substrate structure for use in a liquid crystal assay device in accordance with the invention includes a biochemical blocking compound chemically immobilized on a surface of one side of a support forming a biochemical blocking layer and a biomolecule recognition agent deposited on the side of the support containing the biochemical blocking layer. The biomolecule recognition agent includes a recognition site capable of selectively recognizing a target species to be detected by the liquid crystal assay device. The surface of the side of the support containing the biochemical blocking layer and the deposited biomolecule recognition agent is rubbed such that it possesses features that drive a uniform anchoring of liquid crystals when the liquid crystals contact the side of the support containing the biochemical blocking layer and the deposited biomolecule recognition agent. In another preferred rubbed substrate structure, the surface of the side of the support containing the biochemical blocking layer is rubbed such that it possesses features that drive uniform anchoring of liquid crystals when the liquid crystals contact the side of the support containing the biochemical blocking layer, and the biomolecule recognition agent is deposited on the rubbed surface containing the biochemical blocking layer.
Another rubbed substrate structure for use in a liquid crystal assay device in accordance with the invention, includes: a biochemical blocking layer having biochemicals; a bifunctional spacer compound having a first end and a second end; a surface modifying compound having a first end and a second end; and a support having at least one side that contains the biochemical blocking layer. At least one of the biochemicals is covalently bonded to the first end of the bifunctional spacer compound through a first chemical reaction between a reactive group on the biochemical prior to the first chemical reaction and a reactive group on the first end of the bifunctional spacer compound prior to the first chemical reaction. The surface modifying compound is covalently bonded to the second end of the bifunctional spacer compound through a second chemical reaction between a reactive group on the first end of the surface modifying compound prior to the second chemical reaction and a reactive group on the second end of the bifunctional spacer compound prior to the second chemical reaction. Additionally, the surface modifying compound is covalently bonded to a surface on the side of the support containing the biochemical blocking layer through a third chemical reaction between a reactive group on the surface prior to the third chemical reaction and a reactive group on the second end of the surface modifying compound prior to the third chemical reaction. Finally, the side of the support containing the biochemical blocking layer is rubbed such that it possesses features that drive a uniform anchoring of liquid crystals when the liquid crystals contact the side of the support containing the biochemical blocking layer.
Preferred rubbed substrate structures as described above also include a biomolecule recognition agent deposited on the side of the support containing the biochemical blocking layer. The biomolecule recognition agent has a recognition site capable of selectively recognizing a target species to be detected by the liquid crystal assay device.
In preferred rubbed substrate structures, the bifunctional spacer compound is an organic compound having the following formula before the first and second chemical reactions: 
where n is an integer having a value ranging from 1 to 20, more preferably ranging from 2 to 10, or even more preferably ranging from 5 to 8. Most preferably, the bifunctional activating compound is disuccinimidyl suberate.
In other preferred rubbed substrate structures, the reactive group on the second end of the surface modifying compound before the third chemical reaction is a halogen-silicon bond or an alkoxy-silicon bond whereas in other preferred rubbed substrate structures, the surface modifying compound prior to the second and third chemical reactions is a silicon compound including a silicon atom; an alkoxy group bonded to the silicon atom through an oxygen-silicon bond; and an aminoalkyl group bonded to the silicon atom through a carbon-silicon bond. In still more preferred rubbed substrate structures, the surface modifying compound prior to the second and third chemical reactions is an aminoalkyltrialkoxysilane and more preferably is aminopropyltriethoxysilane.
In still other preferred rubbed substrate structures, the biochemicals of the biochemical blocking layer is a serum albumin, more preferably bovine serum albumin.
In still other preferred rubbed substrate structures the biomolecule recognition agent is an immunoglobulin or a portion of an immunoglobulin whereas in other preferred rubbed substrate structures, the biomolecule recognition agent is a peptide or carbohydrate or a sequence of peptides or carbohydrates, or sequences of DNA or RNA. In still other preferred rubbed substrate structures, the biomolecule recognition agent is capable of recognizing peptides, carbohydrates, DNA, RNA or fragments thereof, or a binding domain associated with a protein, a virus, a bacteria, or a microscopic pathogen.
Still other preferred rubbed substrates are provided in which at least two regions of the surface of the side of the support containing the biochemical blocking layer are rubbed under different pressures or for different lengths such that at least two regions of the surface of the side of the support containing the biochemical blocking layer have different sensitivities towards a target species.
A method for preparing a rubbed substrate structure suitable for use in a liquid crystal assay device includes reacting a biochemical blocking compound having at least one reactive group with an activated modified surface of a support. The activated modified surface of the support has at least one functional group capable of reacting with the reactive group of the biochemical blocking compound such that a covalent bond is formed between the biochemical and the support producing a support with a biochemical-blocking compound containing surface. The method also includes rubbing the biochemical-blocking compound containing surface of the support to produce a rubbed surface possessing features that drive the uniform anchoring of liquid crystals when the liquid crystals contact the rubbed surface.
Preferred methods for preparing a rubbed substrate structure suitable for use in a liquid crystal assay device also include reacting a surface modifying compound having a first end and a second end with a support such that a covalent bond between the support and the first end of the surface modifying compound is formed producing a surface modified support. Preferred methods also include reacting a bifunctional activating agent having a first end and a second end with the surface modified support such that a covalent bond is formed by reaction of the second end of the surface modifying agent with the first end of the bifunctional activating agent producing the activated modified surface of the support.
An optical cell for use in a liquid crystal assay device includes two rubbed substrate structures and a spacing material positioned between the biochemical blocking layers of the two rubbed substrate structures such that the biochemical blocking layer sides of the rubbed substrate structures face each other, but are separated by a cavity that can be filled with a liquid crystal.
A liquid crystal assay device according to the present invention includes a rubbed substrate structure; a surface that uniformly anchors liquid crystals; and a spacing material positioned between the biochemical blocking layer side of the rubbed substrate structure and the surface that uniformly anchors liquid crystals. The surface of the rubbed substrate structure includes both a biochemical blocking layer and a biomolecule recognition agent. In preferred liquid crystal assay devices, the surface that uniformly anchors liquid crystals may be another rubbed substrate structure with a biochemical blocking layer and a biomolecule recognition agent; a rubbed substrate structure that does not contain a biomolecule recognition agent; a glass slide treated with octadecyltrichlorosilane; a rubbed uncoated glass slide; a glass slide with shear-deposited Teflon on it; or a glass slide with an obliquely deposited gold film on it.
Kits for use in a liquid crystal assay include a rubbed substrate structure; a surface that uniformly anchors a liquid crystal; a spacing material, preferably a film, adapted to be placed between the rubbed substrate structure and the surface that uniformly anchors the liquid crystal; and a liquid crystal compound. In a preferred kit for use in a liquid crystal assay, the surface that uniformly anchors the liquid crystal is another rubbed substrate structure. In other preferred kits, the rubbed substrate structure, the surface that uniformly anchors the liquid crystal, and the spacing material are preassembled into a cell with the spacing material placed between them. In such a kit, the sample containing a possible target species would be flushed through the cell for a predetermined amount of time. Next, the liquid crystal would be placed in the cell and may be flushed through the cell, and the kit could thus be used to determine whether the target species was present in the sample.
A method for detecting the presence of a target species using a liquid crystal assay device includes incubating a rubbed substrate structure with a sample to be tested for the presence of the target species; placing a spacing material, preferably a film, between the incubated rubbed substrate structure and a surface that uniformly anchors liquid crystals such that the biochemical blocking layer side of the rubbed substrate structure faces the surface that uniformly anchors liquid crystals; drawing a liquid crystal into the area between the incubated rubbed substrate structure and the surface that uniformly anchors liquid crystals; and determining whether the liquid crystal is uniformly anchored on the rubbed substrate structure.
A device for detecting the presence of more than one target species in a sample is provided. The device includes a support with a rubbed surface having a biochemical blocking layer. The device also include a first target species detection region on a first portion of the support that has the biochemical blocking layer, and the first target species detection region has a first biomolecule recognition agent capable of binding the first target species. The device further includes at least one other target species detection region on at least one other portion of the support having the biochemical blocking layer, and the at least one other target species detection region has at least one other biomolecule recognition agent capable of binding the at least one other target species. The first target species detection region uniformly anchors liquid crystals in the absence of the target species, and the at least one other target species detection region uniformly anchors liquid crystals in the absence of the at least one other target species. The uniform anchoring of liquid crystals in the first target species detection region is disrupted when the first target species detection region is exposed to the first target species, and the uniform anchoring of liquid crystals in the at least one other target species detection region is disrupted when the at least one other target species detection region is exposed to the at least one other target species.
Particularly preferred devices for determining the presence of a target species in a sample are included in which the surface is rubbed while the first biomolecule recognition agent and the at least one other biomolecule recognition agent are respectively present in the first target species detection region and the at least one other target species detection region.
The invention further provides kits for use in detecting the presence of a target species in a sample which kits include at least one rubbed substrate structure and a liquid crystal compound. A method of detecting the presence of a target species in a sample using this type of kit is also provided. The method includes contacting a portion of the rubbed substrate of the kit with a quantity of the sample; placing the liquid crystal of the kit on the portion of the rubbed substrate structure that had contacted the sample; and determining whether the uniform anchoring of the liquid crystal has been disrupted.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.